Fact Sheet 595
Lyme Disease and the Deer Tick in Maryland
Lyme disease is a potentially serious illness
spread by the bite of one type of tick found
on deer and other animals, commonly called
the deer tick. The large human population
in the mid-Atlantic is increasingly at risk
from Lyme disease because of exposure to
deer tick habitat through suburban development on former farmlands and woodlands
and through frequent travel to rural areas
for recreation. In Maryland, changes in land
use have also contributed to an increase in
the state’s deer herd, with a corresponding
increase in the deer tick population.
Complicating the matter further, ticks are
not easily controlled by simply broadcasting
pesticides in their habitat. In addition,
environmental problems caused by pesticide
runoff are becoming as serious as threats
from disease.
The Deer Tick
Ticks are small, flat, bloodsucking pests
more closely related to spiders than to
insects. They do not jump or fly, but they do
cling to vegetation and climb onto passing
animals that brush against them. The deer
Figure 1. Actual size of larva; nymph; fully fed
nymph; unfed adult; and fully fed, adult female.
tick, also known as the blacklegged tick,
Ixodes scapularis Say, is the common carrier of
Lyme disease in the Eastern United States.
Appearance
Ticks have four life stages: egg, larva,
nymph, and adult. The larva is the size of
the period at the end of this sentence. The
nymph is less than one-sixteenth of an inch
long or the size of a pinhead. Nymphs are tan
with black legs and a black shield near the
head. The deer tick is smaller than the familiar dog tick that commonly bites humans.
Unfed adult deer ticks are the size of a sesame
seed. The body of the adult female before
feeding is brick red with black legs and a
black shield at the head. The unfed, adult
male is slightly smaller than the female and
entirely dark. All stages are much larger and
darker when fully fed with blood (Figure 1).
Seasonal Activity
The deer tick requires 2 years to complete
its four life stages. In the spring, each overwintering female lays thousands of eggs. Tiny
larvae hatch from these eggs in late summer.
The larvae do not disperse far; they crawl in
leaf litter or on low vegetation where they
wait for their first host (an animal on which
they can feed). Larval hosts are usually mice
and sometimes other small mammals, birds,
or reptiles. If their hosts are infected with
Lyme disease, ticks become infected from
feeding on the hosts’ blood. Ticks, which
feed only once to complete each stage, need
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Baltimore City
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63
899 cases in Maryland
Maryland Department of Health and Mental
Hygiene, 1999
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Figure 2. Reported cases of Lyme disease in Maryland in 1999 based on victims’ residences.
the nymphs, the adults attach to larger mammal
hosts, such as deer, cattle, horses, dogs, and
humans. After feeding for several days and
mating, the adults drop from their hosts. The
females lay their eggs in the spring and then die.
several days for a full blood meal. As ticks feed,
they swell to several times their unfed size.
Afterwards, the larvae detach and fall to the
ground where they molt to the nymphal stage.
Because the larvae are redistributed or
spread from the hatching site by their hosts,
the newly emerged nymphs are less concentrated than the larvae. These nymphs are
found primarily in small mammal and deer
habitats where the larvae fed the previous
summer and fall. This habitat includes woodlands and regions where grasses and low
shrubs border wooded areas. Nymphs search
higher in the vegetation for hosts than do
larvae. While mice and other small mammals
are still preferred hosts, larger animals, such
as squirrels, raccoons, opossums, dogs, deer,
and humans, may be bitten.
Nymphal ticks are active from April through
August when people are often outdoors. Most
human Lyme disease cases are probably the
result of nymphal tick bites. The majority
of these bites occur in May and June when
nymphal ticks are most abundant. In late
summer, after the nymphal blood meal and
further redistribution, the ticks drop to the
ground, this time molting into the adult stage.
Adults are active in fall, winter, and early
spring whenever temperatures are 50°F or
higher. By climbing higher on plants than
Lyme Disease
Lyme Disease in People
Lyme disease is caused by spiral-shaped
bacteria transmitted by the bite of an infected
deer tick. Most people become ill in the summer when the deer tick nymph is active. An
expanding rash at the site of the tick bite is
the most common sign of Lyme disease. The
rash generally has a reddish edge with more
normal-colored skin in the center. Not everyone who contacts Lyme disease develops this
rash. Other early symptoms of illness are similar to the flu: headache, mild fever, muscle
and joint aches, and fatigue. The rash and/or
the flu-like symptoms usually develop within
1 month of the tick bite.
Lyme disease can be treated with antibiotics.
Treatment is most effective during the early
stage. Untreated, the illness can become more
serious. Symptoms related to the nervous system might develop, such as meningitis, facial
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Low
Moderate
Heavy
Figure 3. Distribution of deer ticks based on the number of ticks found on examined deer.
paralysis, or vision problems. Some people
also develop heart trouble, which can cause
dizziness, fainting spells, or irregular heartbeats. Arthritis, which often affects the knee,
may occur months after the tick bite and
is the most common later complication of
Lyme disease.
ent illness) can be found nearly everywhere
in Maryland, take precautions to reduce the
risk of all tick bites. This is especially important for people who spend a lot of time in
the woods or other areas that support rodents
and other wildlife. Well-planted urban/
suburban areas can also be home to large
numbers of tick hosts.
Lyme Disease in Maryland
Personal Protection
In 1999, the Maryland Department of
Health and Mental Hygiene recorded 899 cases
of Lyme disease (Figure 2). The distribution
of deer ticks corresponds with the pattern of
reported human cases in Maryland (Figure 3).
Although deer ticks have been found in every
county, there appear to be greater numbers in
the counties surrounding the Chesapeake Bay
and on the Eastern Shore. Future studies will
be necessary to determine if deer tick populations are spreading.
Lyme disease is expected to increase in
Maryland. Anyone who spends time in tick
habitat is at risk. Those whose job or recreation involves extended periods of outdoor
activity in tick habitat are at greater risk.
Because deer ticks that carry Lyme disease
bacteria (and other ticks that transmit differ-
Personal precautions against tick bites
remain the best means of reducing the risk of
contracting Lyme disease. Avoid known tickinfested areas whenever possible. If you must
be in tick habitat, take precautions.
Proper Attire
Dress to reduce tick exposure. Wear lightcolored clothes so that the tiny, dark-colored
ticks are easier to see and remove. Wear long
pants tucked into socks or taped to boot tops
and a long-sleeved shirt with the shirttails
tucked in to prevent ticks from getting under
clothing.
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Tick Repellents
prophylactic antibiotic treatment with their
physician if the tick is identified as a potential Lyme vector and was attached for more
than four hours.
Take similar precautions for dogs and other
animals because they also can contract Lyme
disease. For more information on Lyme disease
in animals, ask your county Extension office
for Fact Sheet 534, “Lyme Disease in Animals.”
Use a tick repellent containing permethrin
on clothing and a repellent containing DEET
on skin not covered by clothing. Always
follow label directions.
Permethrin, marketed as Permanone or
Duranon Tick Repellent, kills ticks when
applied to clothing but should not be applied
to skin. Once permethrin has dried on clothing, it remains effective through several
machine washings.
Insect repellents containing DEET may be
applied to exposed skin and clothing to prevent mosquito and tick bites. Concentrations
of less than 100-percent DEET do not repel
ticks as long as pure DEET.
Tick Control
Reducing the number of ticks, and thus
the risk of Lyme disease infection, requires an
integrated program of habitat modification,
host reduction, and, in high-risk areas,
pesticide application.
Tick Checks
Habitat Modification
Frequent and thorough “tick checks”
are essential. Plan specific times for tick
inspection, such as midday and at night.
Check for ticks often and remove them
immediately. When they contact a human
host, ticks wander until they find a feeding
site. They may attach anywhere. Although
unattached ticks cannot transmit disease,
they should also be removed. Nymphal deer
ticks, the stage of most concern to humans,
are small but visible on careful examination.
The tiny larval ticks have not been shown to
transmit Lyme disease.
Removal of attached ticks. Animal
research indicates that a tick must be
attached and feeding for 36 hours before
disease transmission occurs. Therefore, tick
removal in the early feeding period is a
positive step in disease prevention. If a
tick bite occurs, remove the attached tick
promptly. With sharply pointed tweezers,
grasp the tick as close to the victim’s skin as
possible and pull steadily until the tick is
removed.) Neither heat, petroleum jelly, nor
the application of other irritants is recommended for tick removal. Place the tick in
alcohol to preserve it for identification. If
the mouthparts are left in the skin, remove
them and treat the wound with an antiseptic
to prevent other infection. Note the date of
tick removal and see a physician if symptoms
develop. High-risk individuals (e.g., pregnant
women, babies and young children, people
with serious health problems) should discuss
Mice serve as the main reservoir for Lyme
disease and as the primary hosts for the larval
and nymphal stages of ticks. Make an effort to
reduce rodent habitat where possible. Widen
borders of paths and walkways to reduce
their attractiveness to small mammals and to
eliminate human contact with tall grasses and
shrubbery. Keep grassy areas mowed.
Host Reduction
High tick populations are maintained by
high deer populations. Deer are the preferred
host for adult ticks; a reduction of their
numbers should reduce the number of ticks
at all stages, including the nymphal stage.
In controlled experiments, the complete
removal of white-tailed deer from an area
resulted in a gradual drop in tick numbers,
but because hosts other than deer were available, the ticks were not eliminated. Complete
eradication of deer is neither practical nor
desirable in most situations.
Pesticide Application
Damminix. Permethrin-treated cotton
balls in cardboard cylinders, marketed as
Damminix, reportedly reduce tick populations
where white-footed mice are the principal
hosts. White-footed mice use the treated cotton as nesting material. The pesticide does
not harm the mice, but it does kill their tick
parasites. Use this device in early spring and
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late summer to correspond with peak nymphal
and larval feeding. Place the cylinders close
enough together to be available to all female
mice in the area where control is desired.
Since many animals other than mice serve as
tick hosts, Damminix can only be considered
part of a tick control program. Damminix is
a registered pesticide product; follow label
instructions carefully.
Other pesticides. In a residential lot
infested by deer ticks, chemical control in
addition to the habitat and host control may
be necessary. Several pesticides are labeled for
tick control, including carbaryl (Sevin) and
cyfluthrin (Tempo). These pesticides are most
effective when applied to the brushy margins of paths and yards. When it is evident
that ticks are active in these areas, spray low
shrubs and leaf litter thoroughly to kill ticks
that might wander up on this vegetation and
attach to a passing host. Weedy fence lines
that provide cover for rodents can be sprayed
at the base. Broad application of pesticides to
mowed grass is not recommended to reduce
tick populations because neither deer ticks
nor their hosts infest lawns.
Whenever pesticides are used, read and follow label directions to avoid health hazards
and unnecessary harm to the environment.
Apply pesticides carefully and use only when
significant results will be realized. Remember
that all pesticides labeled for tick control are
poisons that kill other organisms as well.
Efforts at area-wide chemical tick control
by aerial spraying have not been effective.
Tree leaves intercept most of the spray, and
ticks are sheltered by vegetation and leaf litter on the forest floor. In addition, pesticide
activity is often short-lived.
Knowledge as Prevention
The best way to protect your family and
pets from Lyme disease is to be aware of highrisk areas and activities and to take preventive
measures. Know how to avoid tick bites, how
to remove ticks and treat bites if they occur,
and how to recognize the symptoms of Lyme
disease. Remember that this disease is treatable, particularly when discovered early.
For more information on Lyme disease, call
your physician, veterinarian, local or state
public health officials, your county Extension
office, or Maryland Cooperative Extension’s
Home and Garden Information Center at
1-800-342-2507.
No endorsement of trade name
products is intended by Maryland
Cooperative Extension.
Addendum
As this publication goes to press, the first
confirmed case of Lyme disease has been
reported in Allegany County.
Lyme Disease and the Deer Tick in Maryland
by
N.L. Breisch, Ph.D.
Faculty Research Associate
Department of Entomology
University of Maryland, College Park
B.L. Thorne, Ph.D.
Associate Professor
Department of Entomology
University of Maryland, College Park
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, University of Maryland, College Park, and local governments.
Bruce Gardner, Interim Director of Maryland Cooperative Extension, University of Maryland.
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Resources Management, Office of the Dean, College of Agriculture and Natural Resources, Symons Hall, College Park, MD 20742.
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